Phosphorylated Sugarcane Bagasse Based Poly (AA-Co-AM) Hydrogel for dual water retention and Controlled NPK Release to enhance drought resilience in Lupine

Background The excessive application of conventional mineral NPK fertilizers has led to severe environmental and agricultural challenges, including nutrient leaching, soil degradation, and ecological risks. To address these issues, there is a critical need for sustainable alternatives that can efficiently manage soil water and nutrients. This study developed a biodegradable NPK hydrogel composite derived from agricultural waste (sugarcane bagasse) to serve the dual purpose of water retention and controlled nutrient delivery. The hydrogel was synthesized by functionalizing sugarcane bagasse via phosphoric acid phosphorylation, followed by graft-copolymerization with acrylamide (AM) and acrylic acid (AA) using free-radical polymerization. Therefore, pot experiments were conducted to evaluate the efficacy of Phosphorylated Sugarcane Bagasse Based Poly (AA-Co-AM) hydrogel on lupine grown under drought conditions. Hydrogel applied at 0, 0.1% and 0.2% (by weight) in pots subjected to water deficit (50% Field Capacity, FC) or sufficiency (100% FC). Results FTIR and SEM analyses confirmed the successful grafting of monomers onto the bagasse and the formation of an interconnected porous architecture. The incorporation of acrylic acid (AA) significantly enhanced the material's water swelling capacity, reaching up to 2900%. A specific hydrogel formulation with an AM:AA ratio of 1:1 demonstrated optimal soil biodegradability, degrading by 25% over 4 weeks. Elemental analysis revealed a high nutrient loading efficiency, which was particularly pronounced for nitrogen in AM-dominant matrices. In a two-season pot trial conducted under deficit irrigation (50% field capacity), the soil incorporation of the H1-type hydrogel at 0.1–0.2% (w/w) significantly improved the growth of lupine ( Lupinus termis L.). Compared to non-amended, drought-stressed controls, the hydrogel-treated plants exhibited increased shoot length (44.42 cm), enhanced chlorophyll and carotenoid content, and higher fresh and dry biomass (23.92 g and 8.32 g, respectively). Additionally, the application of the hydrogel successfully mitigated drought stress, as evidenced by reduced levels of malondialdehyde, hydrogen peroxide, proline, and total soluble sugars, alongside decreased activity of antioxidant enzymes (SOD, CAT, POX). Conclusion This study successfully bridges the gap between agricultural waste valorization and slow-release fertilizer technology. The sugarcane bagasse-based NPK hydrogel composite effectively enhances soil water retention and mitigates the negative physiological impacts of drought stress on plants while providing controlled nutrient delivery. Consequently, this biodegradable hydrogel offers a highly scalable and sustainable strategy to optimize nutrient use efficiency, reduce reliance on conventional mineral fertilizers, and promote resilient agricultural practices.